There was a rolling block musket conversion that came out not long after the end of the Civil War. They have the '66 patent date so would be later than the summer of '66. Caliber was 58 US Musket centerfire. Ammo usually used bar anvil primers. It looks like a rimfire. The 50-70 two band and three band conversions came out about the same time, or very shortly afterward.
There were also the split breech carbines. These look like a rolling block, but the action locks up differently. These were in 46 Ballard and 56-50 Spencer rimfire. The 46 cal. deliveries started in Feb. of '65, while the 50s came in later in '65 after the war was over.
The '67 Navy carbine deliveries started in '68. These were in 50-45 Carbine/Cadet centerfire. This is the same cartridge used in the 1867 Trapdoor cadet rifle and the prototype 1868 Trapdoor carbines. The first delivery was rejected because the rifling was cut too deep, so those RB carbines didn't hit the fleet until 1869 or so. 95 were overruns that were sold on the civilian market, probably in '68. This one would be a good candidate for a an early civilian Rolling Block purchase. They are handy guns, shoot well and are easy to carry on horseback, even thought they don't have a saddle ring.